1. Field of the Invention
The present invention relates to the technology of a calculation device and a calculation method, and more particularly to an operation device and an operation method of obtaining thermo-couple input temperature from thermo-couple output electrical potential and surrounding temperature.
2. Description of Related Art
Conventionally, the expressions of obtaining thermo-couple input temperature are given in an expression 1 (expression (1) is used hereinafter),                     Z        =                                                            c                *                x                            -                                                (                                      y                    +                    273.15                                    )                                4                                      4                    -          273.15                                    (        1        )            
where
c: constant,
x: thermo-couple output,
y surrounding temperature [xc2x0 C.],
z thermo-couple input temperature [xc2x0 C.].
Further, for obtaining thermo-couple input temperature, there is a method of obtaining it by immediately calculating using the required expression (1) and a method of obtaining it by calculating using expression 2 (expression (2) is used hereinafter),
Z=c1+(c2+c3*x)*x+(c4+c5*y)*yxe2x80x83xe2x80x83(2) 
where
C1xcx9cc5: constant,
x: thermo-couple output [V],
Y: surrounding temperature [xc2x0 C.],
z: thermo-couple input temperature [xc2x0 C.],
which is an approximate expression of the expression (1).
Here, FIGS. 6 and 7 are simulation results in which calculations are performed using the expression (1) and the expression (2) in the lower frequency of 520 kHz of the high speed clock. FIG. 7 is a graph of the simulation results expressed in FIG. 6. However, in the conventional calculation method, in order to calculate the expression (1), it is required to perform multiplication/division calculation thrice, adding/subtraction calculation thrice, and square root calculation twice. Here, for each individual calculation, multiplication/division calculation requires 17 msec, adding/subtraction calculation requires 0.4 msec, and square root calculation requires 25 msec. Namely, in order to calculate the expression (1), total calculation requires 102.2 msec. Here, according to the expression (1), in the case where thermo-couple output electrical potential is 0.02 [V] and the surrounding temperature is 18 [xc2x0 C.], thermo-couple input temperature is 122.83 [xc2x0 C.].
On the other hand, in order to calculate the expression (2), it is required to perform multiplication/division calculation thrice, adding/subtraction calculation thrice, and square root calculation twice. Namely, in order to calculate the expression (2), total calculation requires 69.2 msec. Here, according to the expression (2), in the case where thermo-couple output electrical potential is 0.02 [V] and the surrounding temperature is 18 [xc2x0 C.], thermo-couple input temperature is 121.89 [xc2x0 C.].
In this way, when calculation is performed using the expression (1), calculation requires 102.2 msec, although the value of thermo-couple input temperature that is required is accurate. On the other hand, when calculation is performed using the expression (2), the result of calculation becomes 121.89 [xc2x0 C.] by causing an error of 0.94 [xc2x0 C.] from the expression (1) although calculation requires 69.2 msec by a reduction of 33 msec.
Namely, the time for calculation becomes long although the result of the calculation is accurate when the expression (1) is calculated, and the result of the calculation causes an error although the time for the calculation becomes short when the expression (2) is calculated.
The purpose of the present invention is to provide a calculation device and a calculation method in which the error caused in the results of the calculation is reduced as much as possible and the time for calculation is small.
The summary of representatives is explained in the following based on the inventions disclosed in the present application.
A calculation device of the present invention, in which thermo-couple input temperature is calculated from thermo-couple output electrical potential and the surrounding temperature, includes a memory for storing a plurality of values of thermo-couple input temperature being calculated using a plurality of values of thermo-couple output electrical potential and a plurality of values of surrounding temperature; and a calculation unit for inputting a predetermined value of thermo-couple output electrical potential and a predetermined value of surrounding temperature, reading out from the memory a plurality of values of stored thermo-couple output electrical potential corresponding to a predetermined value of inputted thermo-couple output electrical potential, reading out from the memory a plurality of values of stored surrounding temperature corresponding to a predetermined value of inputted surrounding temperature, reading out from the memory a plurality of values of stored thermo-couple input temperature selected from a plurality of values of read out thermo-couple output electrical potential and a plurality of values of read out surrounding temperature, and calculating thermo-couple input temperature corresponding to a predetermined value of inputted surrounding temperature and a predetermined value of inputted thermo-couple output electrical potential using an interpolation.
In accordance with the above-described system arrangements, it is possible to reduce an error caused in the results of calculation as much as possible and shorten the time for calculation as much as possible.